470 ECHIKODERMATA. 



the vesicular feet of the preceding order. Their body is invested with a cori- 

 aceous unarmed skin. Several points of their_ internal structure are not well 

 understood. In 



MOLPADIAJ Cuvier, 



As in Holothuria, we find a coriaceous body forming a thick cylinder open at 

 both ends, and a tolerably similar internal organisation ; but, independently of 

 the want of feet, the mouth is destitute of tentacula, and is provided with an 

 apparatus of bony parts, but less complicated than that of the Echini. 



jMiNYAS, Cuvier, 



Where the body is also destitute of feet, and open at both extremities; but its 

 form is that of a spheroid depressed at the poles, and furrowed like a melon. 

 I can find no armature about the mouth. 



PRIAFULUS, Lamarck, 



Where the body is cylindrical and transversely marked with deep annular 

 ruga, terminated anteriorly by an elliptical mass, slightly wrinkled longitu- 

 dinally, perforated by the mouth, and posteriorly by the anus, from which 

 issues a thick bundle of filaments which may be organs of generation. The 

 interior of the mouth is provided with a great number of extremely sharp and 

 horny teeth arranged in quincunx, and directed backwards ; the intestine pro- 

 ceeds in a straight line from the mouth to the anus. The muscular system 

 resembles that of the Holothurise. 



LITHODERMIS, Cuvier, 



Where the body is oval and compressed posteriorly ; its surface has the 

 appearance of being covered with a layer of stony granules, which form an 

 extremely indurated crust. The mouth is surrounded with tentacula, and the 

 intestines seem to be analogous to those of the Holothuriae. They have no 

 anus that I can perceive. 



SIPUNCULUS, Gmelin. 



The body is cylindrical and elongated, the skin thick and wrinkled in both 



directions. The mouth is provided with a 

 sort of proboscis susceptible of retraction and 

 protrusion by the action of large internal 

 muscles, and the anus is more or less approx- 

 imated to the base of that organ. The intestine proceeds from the mouth to 

 near the opposite extremity, and then returns, twining spirally round itself. 

 The only matters found in it are sand and fragments of shells. Numerous 

 vessels appear to unite it with the external envelope, besides which a thread 

 extends along one of its sides which may possibly be nervous. Two long 

 bursse, situated anteriorly, open exteriorly a little below the anus, and near 

 this last orifice, internally, we sometimes find a bundle of ramous vessels 

 which may be organs of respiration. 



